Bilirubin is the waste product that results from the breakdown of hemoglobin molecules from worn out red blood cells. Ordinarily, it is excreted from the body as the chief component of bile. Excessive levels of bilirubin stain the fatty tissues in the skin yellow; this condition is called jaundice. Very high levels of bilirubin in the bloodstream can cause permanent damage to certain areas of the brain of newborn infants - kernicterus. This can cause a characteristic form of crippling known as athetoid cerebral palsy. To prevent this from happening, bilirubin levels are monitored in newborns, and excessive levels of bilirubin are treated by either phototherapy ("bilirubin lights") or exchange transfusion.